When using rechargeable batteries in electrical or electronic systems, the ability to extend the period of a rechargeable battery's charge and overall battery life is valuable. Existing charging systems typically charge a battery to the same fixed charge voltage each time that the battery is recharged. The manufacturer's recommended charge voltage is typically selected to maximize initial battery run time. In contrast, reducing the charge voltage of a rechargeable battery cell (e.g., lithium ion) can provide a longer life, especially when the rechargeable battery is exposed to higher environmental temperatures. However, a system designed with a battery charger that charges to a fixed lower initial voltage to provide a longer life cannot utilize the full capacity of the battery when the use case and environmental conditions may change, thus cutting the discharge time shorter than is desirable for many use cases.